The Wako Group (Hiroshima City, Hiroshima Prefecture), which is engaged in entertainment facility management and real estate business, is operating two mega- (large-scale) solar power plants at industrial parks in Hiroshima Prefecture. They are the "Hiroshima By-Airport Industrial and Distribution Park Solar Power Plant" with 1.99MW output and the "Ujigami Industrial Park Solar Power Plant" with 2.98MW output (Fig. 1).

The Wako Group decided to purchase unused sites in the two industrial parks, which had consulted its Real Estate Department about effective use of these sites, and construct the mega-solar power plants there. The sites were located in Hiroshima By-Airport Industrial and Distribution Park in Higashihiroshima City and Ujigami Industrial Park in Kitahiroshima-cho.

Because the construction of these two mega-solar power plants progressed almost at the same time, the Wako Group could easily boost efficiency by managing the necessary applications, negotiations and contracts for the two plants in parallel.

Chudenko Corp provided the engineering, procurement and construction (EPC) services. As these were the first solar power plant projects based on the feed-in tariff (FIT) program that Chudenko had engaged in, the company focused on them as its model business and has published their pictures in its promotional materials.

Of the related equipment and materials it procured, Chudenko used Solar Frontier KK's solar panels via Orix Corp in view of its business relationship with Orix. As for PV inverters, Chudenko used those of Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC) (Fig. 3).

Both the solar panels and PV inverters were attractive because of their good balance between the capacity, the high conversion ratio and the price.

"It is difficult for a power generation system and a construction method that gives priority to cost and nothing else to stabilize the project for a period as long as 20 years and maximize the profit," Administrative Manager Tadaharu Ohshimo of the Wako Group said. "The investment efficiency could be boosted more by constructing a solid plant and realizing stable power generation."

Measures against snow cover in Kitahiroshima-cho

Even though the two plants were constructed almost simultaneously using the same facilities, they are different in some parts. This is because Kitahiroshima-cho, where the Ujigami Industrial Park is located, is an area that has snow cover in winter.

The solar panels were tilted by 20° in Kitahiroshima-cho whereas the angle was 10° in Higashihiroshima City (Fig. 4). The height of the panel's ground side was also raised to about 80cm.

Protection from snow cover was one of the reasons why Chudenko adopted Solar Frontier's solar panels. The gap between the edge of this panel and the cover glass is smooth and helps the snow on the panel slip off (Fig. 5).

It seldom snows as much as in the heavy snow areas in eastern Japan. However, the snow cover in the winter of 2013 and 2014 could have affected the power generation without these measures, and Chudenko considers they have been effective.

Automatic recovery from suspension caused by voltage phase jump

Since the plant started operation, some unexpected problems have occurred. For example, the PV inverters at the mega-solar power plants frequently automatically stopped due to fluctuations in the frequency and voltage of the current running the transmission cables of Chugoku Electric Power Co Inc, and the plants could not sell power when it was generated.

This was because the "voltage phase jump detection mode" had worked. This mode is one of the PV inverter's capabilities to prevent isolated operation, and it was accidentally proved that the mode was sufficiently functioning. However, although the party to be blamed was not the mega-solar company but the electric power company, the mega-solar company had to request confirmation from the power company and manually recovered the operation every time the grid connection was automatically cut. For power producers, it would be much easier if automatic recovery of the operation were allowed.

Based on these circumstances, two measures have been applied. One is the notification that is sent to the smartphones of Manager Ohshimo and the related staff on the power producer side when the mode to stop isolated operation works and PV inverters stop automatically. TMEIC enabled this by adding dedicated software.

The other is the permission for automatic operation recovery that the plants negotiated with and acquired from Chugoku Electric Power regarding the PV inverters' automatic termination caused by voltage phase jump problems.

Vines bring down fence

At the mega-solar plant in Higashihiroshima City, weeds have grown more than expected (Fig. 6). They not only thrived across the site but also grew over the fence on the north side and eventually became like a wall of vines. Then, strong winds hit the area, and the fence collapsed.

While adding support pillars to the replaced fence to prevent it from falling down again, the plant decided to subdue the growth of vines by covering the ground with gravel (Fig. 7).

As a monitoring camera was struck by lightning, the plant is considering setting up lightning rods.